1. Field of the Invention
This invention relates to the field of communications, and, more particularly, to allocation of resources of a communications network for supporting wireless communications.
2. Description of the Related Art
Mobile communications broadly encompass the various devices and techniques that enable individuals to communicate without having to rely on a static network infrastructure. Laptop computers, palmtops, personal digital assistants (PDAs), and cellular phones are all part of the growing array of computing and telephony-based mobile devices that can be used to exchange voice signals and digitally encoded data from remote locations. The general architecture for mobile systems entails mobile nodes, or hosts, communicating with one another through a series of base stations that serve distinct zones or cells. According to this architecture, a mobile node remains in contact with a communication network by repeatedly tearing down old connections and establishing new connections with a new base station as the host moves from one cell to another.
What is generally needed for such architectures to function adequately is some way for the mobile node to let other nodes know where the mobile node can be reached while the host is moving or located away from home. In accordance with a typical mobile networking protocol, a mobile node registers with a home agent so that the home agent can remain a contact point for other nodes that wish to exchange messages or otherwise communicate with the mobile node as it moves from one location to another. An example of such a protocol is Mobile Internet Protocol (Mobile IP). Mobile IP allows a mobile node to use two IP addresses, one being a fixed home address and the other being a care-of address. The care-of address changes as the mobile node moves between networks thereby changing its point of attachment to a network. When the mobile node links to a network other than one in which the home agent resides, the mobile node is said to have linked to a foreign network. The home network provides the mobile node with an IP address and once the node moves to a foreign network and establishes a point of attachment, the mobile node receives a care-of address assigned by the foreign network.
Mobile IP v. 4 depends on the interaction between a home agent and foreign agents, the foreign agents serving as wireless access points distributed throughout a coverage area of a network or an interconnection of multiple networks. This architecture, however, does have disadvantages. These have led to assorted proposals for enhancing the capabilities of Mobile IP. One such proposal is to use a hierarchy of foreign agents intended to reduce the number of registrations required for the mobile node.
FIG. 1 is a schematic diagram illustrating an exemplary architecture for a mobile communications system 100 using hierarchical foreign agents as is known in the art. As shown, the system 100 can include a home agent 105 and a foreign agent 110, each communicatively linked via a communications network 115 such as the Internet. The foreign agent 110 further is communicatively linked with the hierarchy of foreign agents 120, 125, 130, 135, 140, and 145. Accordingly, a mobile host 150 can choose a foreign agent which is closer than the others as a registration point. Registration messages are constrained to that region only.
The mobile node 150 travels in range of foreign agent 145. The mobile node 150 registers with foreign agent 145, foreign agent 125, and foreign agent 110 as the mobile node's 150 care-of addresses. A registration request also reaches the home agent 105. The registration reply reaches the mobile node 150 via the reverse path. Accordingly, packets received at the home agent 105 that are to be routed to the mobile node 150 can be tunneled to foreign agent 110, which tunnels the packets to foreign agent 125, and finally to foreign agent 145 prior to transmitting the packets to the mobile node 150.
Nevertheless, registration delays and associated information losses can still represent significant obstacles for wireless communications involving a mobile node. This stems mainly from the inevitable delay associated with the setting up of a new communication link each time the mobile node is handed off from one foreign agent to another. The setup requires time for the network to negotiate protocol details, establish communication rates, and decide the applicable error-handling approaches to be employed. These should each be resolved as a prelude to establishing the actual connection for the exchange of data. With conventional systems and devices, the setting up typically must await the arrival of the mobile node in the predefined region of coverage for the foreign agent to which the mobile node is to be handed off. Depending upon the mobile network configuration, the time required for registration can rival the time in which the mobile node dwells within a given cell coverage area. Moreover, data packets may be lost if they arrive for the mobile node during the time in which the setup is being worked out.